Mississippi. A big primary there. And ABC's Jeff Zeleny was covering it. Reporter: A bizarre senate race has the tea party boiling. There is something a bit unusual about a republican primary that is decided by liberal democrats. Reporter: Chris Mcdaniel is not backing down after losing to Thad Cochran. Cochran made no secret and no apology for reaching out to african-americans, union workers, and other democrats to win. We all have a right to be proud of our state tonight. Reporter: Asking for democratic votes is not a violation of Mississippi law. Accusations of voter fraud have fired up conservatives. I wonder what the campaign slogan was in Mississippi the last couple of days. Uncle Toms for Thad? Reporter: The fight took a stranger turn Friday. A Mississippi tea party leader committed suicide. He had been arrested for breaking into the nursing home of senator Cochran's wife. Ken cuccinelli, a leader of the conservative movement, says the fallout goes well beyond Mississippi. The conservative grass roots is not going to tolerate this. They're going to risk ongoing trench warfare. Reporter: The win inkress tcreases the odds of taking back the senate. But president Obama told George he thinks democrats will keep the majority. I think they'll retain the majority. Reporter: It's an uphill climb toward November. This win by Thad Cochran surprised a lot of people. Did it surprise you? A little bit. The momentum in the republican party is not with Thad Cochran. It's with the tea party. One big win against Eric Cantor. Right? Yeah, but they have nominated a lot of in nominees, in many state, that are acceptable to the tea party and the establishment. They're running much more P populist campaigns. I very much -- Marco Rubio, who gave speeches last week, Ted Cruz, Scott walker, all those people can run against Hillary Clinton as spokesmen for middle class Americans. Working class Americans. That is a huge change for the tea party. They're changing the republican party. Changing the republican party. Explain to me how Thad Cochran, the conservative republican, got african-american democrats in Mississippi to vote for him. In 1964, he voted for Lyndon Johnson. In 1972, he ran against a conservative segregationist democrat. Beat him. Hired the first african-american please stand by. Ane Katrina. That and many other reasons. He had reasons to go after these votes in the high-producing black counties. That's why, I think, he won. I think there is an irony because this is the 50th anniversary of the freedom summer campaign to register african-americans. You have a party that has worked to roll back voting rights. You're facing the greatest curve of voting rights since reconstruction. Here, you have Thad Cochran put over the top by african-american voters. He might have to resist those calls to curve that. But also what he did. Donna told me this. He also spoke of government as a force for good. There were adds up. Trent Lott. You can eat pork, you can't eat tea. I'm happy to go to the voters in 2016 on that issue. This is a phyrric victory. It's only going to engage more energy in this. It looks like the republican party in Mississippi wanted to go one direction. The establishment said, no, no. We love the status quo. We love the status quo. Let's not do that. If by Thad Cochran winning, it will change the way he behaves in office, then god bless him. If all of this was a cynical attempt to win an election, then god save him.

This transcript has been automatically generated and may not be 100% accurate.

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